A hold down mechanism can be used with a variety of furnace types including, for example, induction furnaces. To summarize, an induction furnace can melt an alloy charge placed within a crucible of the furnace by applying a primary electric current to electrically conductive furnace coils that surround the crucible. The primary current induces a secondary current within the charge; this secondary current meets electrical resistance in the charge, which generates heat. When sufficient heat is generated, the alloy charge melts. In operation, an induction furnace can reach temperatures that range from approximately 1000° F. to approximately 3300° F.
A heat-resistant, refractory lining is often positioned in the crucible of the furnace to hold the molten charge and the hot gases. The lining can be secured to an interior surface of the crucible, for example. Refractory linings used in induction furnaces are usually composed of oxides of materials such as, for example, silica (SiO2), alumina (Al2O3), and/or magnesia (MgO). The appropriate refractory material for a particular furnace depends on the metallurgical requirements, operating temperatures, and type of melting operations. Due to the high temperatures within the furnace, the refractory lining is often a consumable material that erodes or becomes otherwise damaged over time. When the lining has been consumed and/or damaged to a particular extent, the refractory lining is replaced. An induction furnace in an industrial facility may be relined several times per year, for example.
A hold down mechanism is often used to secure a refractory lining to an induction furnace. When the crucible of the furnace is tilted to empty the crucible contents, i.e., the molten alloy charge, the hold down mechanism can retain the refractory lining in the crucible, for example. The hold down mechanism can be releasably secured to the furnace by fasteners. For example, bolts can secure the hold down mechanism to the body of the furnace. As the furnace generates heat, the hold down mechanism can be subjected to extremely high temperatures, which can cause thermal expansion of the hold down mechanism or parts thereof. The thermal expansion can, in turn, cause the hold down mechanism to buckle and/or warp between fasteners. Once warped to a certain degree, the hold down mechanism no longer operates properly and should be replaced with a new or rebuilt hold down mechanism. The hold down mechanism is often replaced each time the furnace is relined; for example, the hold down mechanism can be replaced four times per year on a furnace that is relined four times per year. Replacement of the hold down mechanism can significantly add to the maintenance costs of the furnace. A new hold down plate for an induction furnace in an industrial facility may cost approximately $5,000 or more, for example. Thus, if a furnace is relined four times per year, replacement of the hold down mechanism can add $20,000 or more to yearly furnace maintenance costs.
Hold down mechanisms can comprise reinforcing features intended to prevent or limit warping of the hold down mechanism in the region between fasteners. The reinforcing features can include arms, ribs and/or shoulders, for example, on the hold down mechanism. Even if reinforcing features are provided, warping of the hold down mechanism can still occur, especially at higher temperatures. For example, warping of hold down mechanisms including reinforcing features has been observed at operating temperatures above approximately 2000° F.
In an effort to reduce maintenance expenses, warped hold down mechanisms may be rebuilt and reinstalled. Rebuilding a warped hold down mechanism can afford cost savings over complete replacement of the hold down mechanism. However, rebuilding a hold down mechanism can be difficult and may still be expensive. Furthermore, a hold down mechanism can be warped to such a degree that rebuilding the mechanism is impractical.
Accordingly, it would be advantageous to provide a hold down mechanism that is less susceptible to warping from the high temperatures common to operation of an induction furnace. Further, it would be advantageous to provide a hold down mechanism that can be reinstalled and reused when the furnace is relined. More generally, it would be advantageous to provide an improved hold down mechanism for releasably holding a refractory lining relative to a furnace.